A vibrating device which includes a diaphragm vibrated by driving a piezoelectric film is used in a flat speaker or a haptics device (a tactile sense presenting device) as described, for example, in WO2012-0157691.
FIG. 9(A) is a side view of a vibrating device 101 employing a conventional configuration, and FIG. 9(B) is a top view of the vibrating device 101. The vibrating device 101 includes a piezoelectric film 102, a diaphragm 103 and frame members 104 and 105. The diaphragm 103 and the piezoelectric film 102 have rectangular shapes which are elongated in a length direction (the vertical direction as viewed in FIG. 9(B)). The piezoelectric film 102 is formed by stretching a PLLA (poly-L-lactic acid) film in a stretching direction (indicated by outlined arrows in FIG. 9(B)) and cutting the stretched PLLA film out in such a manner that the length direction of the piezoelectric film 102 forms a 45° angle with respect to the stretching direction. The piezoelectric film 102 formed in this way stretches and contracts in the width direction when a voltage is applied thereto. The frame members 104 and 105 are provided at opposite ends of the piezoelectric film 102 and extend in the length direction. Opposite ends of the diaphragm 103 are connected to the piezoelectric film 102 by the frame members 104 and 105, respectively. The diaphragm 103 flexes such that a center of the diaphragm 103 in the width direction is spaced apart from the piezoelectric film 102 (see FIG. 9(A)) and that the frame members 104 and 105 apply a tensile force to the piezoelectric film 102 in the direction of the solid arrows in FIG. 9(a). When an AC voltage is applied to the piezoelectric film 102, it vibrates in the width direction and the curvature of the diaphragm 103 fluctuates along with this vibration.
In the haptics device of FIGS. 9(A) and 9(B), a downward pressing force applied to the diaphragm 103 in the thickness direction may cause the diaphragm to flatten and become parallel to the piezoelectric film. When this happens, the diaphragm barely vibrates even when the piezoelectric film is vibrated in the width direction (the horizontal direction in FIG. 9(A)). As a result, it is difficult to provide the user with a tactile feedback. To prevent the diaphragm from being pushed and flattened, the diaphragm may be made thick and rigidity of the diaphragm may be improved. However, when this is done, the amount of the diaphragm bends becomes small and it is difficult to provide a tactile feedback to the user.
It is therefore an object of the present invention to provide a vibrating device and a tactile sense presenting device which can bend a diaphragm in a thickness direction from a flat state and can easily increase the amount the diaphragm bends in response to the vibration of the piezoelectric film.